Meanwhile, a notice on a silent street protest in Warsaw planned for Tuesday afternoon, organised by “Stop ACTA” campaigners on Facebook, attracted more than 38,000 “like” tags.

The fresh wave of protest comes after weekend anti-ACTA cyber attacks by the groups Anonymous and Polish Underground took down official websites belonging to Poland’s president, prime minister, parliament and foreign and culture ministers.

The prime minister’s website (www.kprm.gov.pl) was still down Tuesday, with links directing users to his official Blip, Facebook and Twitter pages.

An attack early Monday morning left the message “Hacked by the Polish Underground: Stop ACTA” appear on it.

Under a vast Internet anti-piracy campaign launched over 18 months ago, US authorities have seized more than 350 website domain names, including a spectacular global swoop on file-sharing site Megaupload.com.

But US congressional leaders put strict anti-online piracy legislation on hold following a recent wave of protests led by Google and Wikipedia denouncing the bills as a threat to Internet freedom.